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<title>Berkeley DB Reference Guide: Windows notes</title>
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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Building Berkeley DB for Windows systems</dl></b></td>
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<p align=center><b>Windows notes</b></p>
<ol>
<p><li>Berkeley DB does not support the Windows/95 platform.
<p><li>Berkeley DB does not support replication on the Windows/98 or Windows/ME
platforms.
<p><li>On Windows/98 and Windows/ME, files opened by multiple processes do not
share data correctly.  For this reason, the <a href="../../api_c/env_open.html#DB_SYSTEM_MEM">DB_SYSTEM_MEM</a> flag
is implied for any application not specifying the <a href="../../api_c/env_open.html#DB_PRIVATE">DB_PRIVATE</a>
flag, causing the system paging file to be used for sharing data.
<p><li>On Windows/98 and Windows/ME, removing or renaming a file using the
<a href="../../api_c/env_dbremove.html">DB_ENV-&gt;dbremove</a>, <a href="../../api_c/env_dbrename.html">DB_ENV-&gt;dbrename</a>, <a href="../../api_c/db_remove.html">DB-&gt;remove</a> or
<a href="../../api_c/db_rename.html">DB-&gt;rename</a> methods may fail if another thread of control has the file
open for any reason, including checkpointing or flushing pages from the
underlying shared database environment cache.  There is no workaround
for this problem other than re-attempting the operation after the other
thread of control has closed its Berkeley DB handles.
<p><li>On Windows, system paging file memory is freed on last close.  For this
reason, multiple processes sharing a database environment created using
the <a href="../../api_c/env_open.html#DB_SYSTEM_MEM">DB_SYSTEM_MEM</a> flag must arrange for at least one process to
always have the environment open, or alternatively that any process
joining the environment be prepared to re-create it.
<p>If a system memory environment is closed by all processes, subsequent
attempts to open it will return an error.  To successfully open a
transactional environment in this state, recovery must be run by the
next process to open the environment.  For non-transactional
environments, applications should remove the existing environment and
then create a new database environment.</p>
<p><li>When using the <a href="../../api_c/env_open.html#DB_SYSTEM_MEM">DB_SYSTEM_MEM</a> flag, Berkeley DB shared regions are
created without ACLs, which means that the regions are only accessible
to a single user.  If wider sharing is appropriate (for example, both
user applications and Windows/NT service applications need to access
the Berkeley DB regions), the Berkeley DB code will need to be modified to create
the shared regions with the correct ACLs.  Alternatively, by not
specifying the <a href="../../api_c/env_open.html#DB_SYSTEM_MEM">DB_SYSTEM_MEM</a> flag, filesystem-backed regions
will be created instead, and the permissions on those files may be
directly specified through the <a href="../../api_c/env_open.html">DB_ENV-&gt;open</a> method.
<p><li>Applications that operate on wide character strings can use the
Windows function WideCharToMultiByte with the code page CP_UTF8 to
convert paths to the form expected by Berkeley DB.  Internally, Berkeley DB calls
MultiByteToWideChar on paths before calling Windows functions.
<p><li>Various Berkeley DB methods take a <b>mode</b> argument, which is intended
to specify the underlying file permissions for created files.  Berkeley DB
currently ignores this argument on Windows systems.
<p>It would be possible to construct a set of security attributes to pass to
<b>CreateFile</b> that accurately represents the mode.  In the worst
case, this would involve looking up user and all group names, and creating
an entry for each.  Alternatively, we could call the <b>_chmod</b>
(partial emulation) function after file creation, although this leaves us
with an obvious race.</p>
<p>Practically speaking, however, these efforts would be largely meaningless
on a FAT file system, which only has a "readable" and "writable" flag,
applying to all users.</p>
</ol>
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